Rotary machine with seal

ABSTRACT

The so-called comb-type labyrinth sealing device (S 1 ) is disposed in a gap between a rotor blade ( 2 ), i.e. a rotating member, and a labyrinth packing ( 9 ), i.e. a stationary member. The sealing device (S 1 ) has a plurality of sealing fins (F 1,  F 2 ) arranged on the opposite sides of the gap opposite to each other. The sealing fins are axially spaced apart at unequal pitches, and hence a possibility that some of the clearances between the opposite sealing fins (F 1,  F 2 ) decrease when a casing holding the labyrinth packing ( 9 ) and a rotor ( 1 ) are axially displaced relative to each other due to the difference in thermal expansion between the rotator and the casing increases.

TECHNICAL FIELD

[0001] The present invention relates to a rotary machine, such as anaxial-flow turbine, and, more particularly, to improvements in a sealingdevice between stationary and rotating members of a rotary machine.

BACKGROUND ART

[0002] It has been desired to reduce, to the least possible extent, theleak rate of a working fluid that leaks through gaps between stationaryand rotating members of rotary machines, such as axial-flow turbinesincluding steam turbines and gas turbines.

[0003]FIG. 8 shows a general steam turbine, i.e. a rotary machine. Thissteam turbine has a turbine rotor 1 provided with rotor blades 2, i.e.rotating members, and a turbine casing 6 enclosing outer rings 3 of anozzle diaphragm, stator blades (turbine nozzles) 4, and inner rings 5of a nozzle diaphragm, i.e. stationary members. Opposite ends of therotor 1 are supported in bearings 11. Noncontact sealing devices areinterposed between each of the rotor blades 2 and each of the outerrings 3, and between the rotor 1 and each of the inner rings 5 toprevent the leakage of the working fluid.

[0004]FIG. 9 is an enlarged view of a part of FIG. 8 showing such asealing device by way of example. Referring to FIG. 9, the outer ring 3of the nozzle diaphragm holds a labyrinth packing 9 provided with aplurality of chip fins 7 extending toward the outer edge of the rotorblade 2. The inner ring 5 of the nozzle diaphragm 5 holds a labyrinthpacking 10 provided with a plurality of sealing fins 8 extending towardthe rotor 1.

[0005] The so-called hi-lo labyrinth sealing device, which is differentfrom the sealing device shown in FIG. 9, has a protrusion disposed onone side, i.e. the rotating side or the stationary side, of a gap, and aplurality of sealing fins disposed on the other side of the gap. Thesealing fins are arranged axially at equal pitches. The so-calledcomb-type labyrinth sealing device shown in FIG. 10 is used. Thecomb-type labyrinth sealing device shown in FIG. 10 has a plurality ofsealing fins F1 and F2 disposed on the opposite sides of a gap,respectively, so as to extend toward each other. The fins F1 arearranged axially at equal pitches P2, and the fins F2 are arrangedaxially at equal pitches P1.

[0006] A rotary machine using a high-temperature working fluid, such asa steam turbine, undergoes temperature changes between starting andstopping and, consequently, the casing and the rotor of the rotarymachine are displaced axially relative to each other due to thedifference in thermal expansion, i.e. the difference in elongation,between the casing and the rotor. Generally, the rotor and the casinghave different heat capacities, respectively, and the axial elongationof the casing is smaller than that of the rotor. Consequently, the rotorand the casing are displaced axially relative to each other.

[0007] In the comb-type sealing device as shown in FIG. 10, the sealingfins F1 and F2 do not come into contact with each other even if therotor and the casing are displaced axially relative to each other due tothe difference in thermal expansion between the rotor and the casing. Onthe other hand, the sealing performance of this comb-type sealing deviceis very high while the clearances between the corresponding sealing finsF1 and F2 are kept at a minimum. When the sealing fins F1 and F2 aredisplaced axially relative each other due to the difference in thermalexpansion between the rotor and the casing, the clearances increase andthe sealing performance of the comb-type sealing device deterioratessharply.

[0008] The deterioration of the sealing performance due to thedifference between the rotor and the casing in thermal expansion may becompensated for by axially arranging many sealing fins. However, thepossible number of stages of the sealing fins is limited because theblowby of the fluid flowing in a sealing part occurs if the number ofthe stages of the fins is greater than a certain limit.

[0009] The sealing effect of the sealing device shown in FIG. 9 ishigher when the clearances between the edges of the tip fins 7 and thesealing fins 8, and the rotating members 2 and 1 are smaller. However,it is possible that the edges of the fins 7 and 8 come into contact withthe rotating members 1 and 2, and there by the fins 7 and 8, and therotating members 1 and 2 are damaged if the clearances are excessivelysmall.

[0010] The variation of the clearances due to thermal deformation duringthe operation of the rotary machine is the principal factor of such atrouble resulting from contact between the members. Such a variation ofclearances occurs mostly at the start and stop of the rotary machine orwhen the load on the rotary machine changes. Therefore, if the size ofthe clearance is determined on the basis of conditions for operationsother than those for the rated operation of the rotary machine, theclearances increase unnecessarily during the rated operation and,consequently, the leak rate of the working fluid increases. A movablesealing mechanism capable of changing clearances in a sealing partaccording to the operating condition is necessary to solve such aproblem. A rotary machine provided with such a movable sealing mechanismis disclosed in, for example, JP61-16209A (1986). In addition, FIGS. 11to 14 show known movable sealing mechanisms.

[0011]FIGS. 11 and 12 show the so-called hi-lo labyrinth sealing deviceincluding ridges 15 formed on the side surface of a rotor 1. A labyrinthpacking 10 integrally provided with fins 13 is mounted on the inner ring5 of a nozzle diaphragm. A proper radial clearance e is maintainedbetween the fin 13 and the ridge 15 by the resilience of a plate spring14 interposed between the labyrinth packing 10 and the inner ring 5 ofthe nozzle diaphragm.

[0012] A hi-lo labyrinth sealing device shown in FIGS. 13 and 14includes a labyrinth packing 10 provided with circumferential grooves16, and coil springs 17 placed in the circumferential grooves 16 of thelabyrinth packing 10. In this hi-lo labyrinth sealing device, the radialclearance e between a fin 13 and a ridge 15 is regulated by the pressureof steam ST supplied through a groove 18 to the labyrinth packing 10,and the resilience of the springs 17 pressing the labyrinth packing 10radially outward.

[0013] In those movable sealing mechanisms, the labyrinth packing 10 ismoved radially with respect to the rotor 1. Thus, those movable sealingmechanisms are not provided with any measures for coping with therelative axial displacement of the casing and the rotor due to thedifference between the casing and the rotor in thermal expansion(thermal elongation).

[0014] Therefore, in the rotary machines provided with those sealingmechanisms are obliged to arrange the plurality of ridges 15 axially atcomparatively big pitches to avoid contact between the fins 13 and theridges 15. The axial arrangement of the ridges at big pitches reducesworking fluid sealing effect.

DISCLOSURE OF THE INVENTION

[0015] The present invention has been made in view of the foregoingproblems and it is therefore an object of the present invention toprovide a rotary machine provided with a sealing device capable ofsuppressing the reduction of sealing performance resulting from therelative axial displacement of a rotary member and a stationary memberdue to the difference between the rotary member and the stationarymember in thermal expansion.

[0016] According to the present invention, there is provided a rotarymachine comprising: a rotating member supported for rotation about anaxis of rotation; a stationary member surrounding the rotating member;and a sealing device disposed in a gap between the rotating member andthe stationary member, wherein the sealing device includes a pluralityof sealing fins arranged opposite to each other on the opposite sides ofthe gap, and at least the sealing fins arranged on one side of the gapare axially spaced apart at unequal pitches.

[0017] According to this rotary machine, at least the sealing fins onone side of the gap are axially spaced apart at unequal pitches, andhence a possibility increases that some of the clearances between theopposite sealing fins decrease when the rotating member and thestationary member are axially displaced relative to each other due tothe difference in thermal expansion between the rotating member and thestationary member. Therefore, the sealing device of this rotary machine,as compared with the sealing device in which all the sealing fins arearranged at equal pitches, is capable of suppressing the deteriorationof sealing performance resulting from the relative axial displacement ofthe rotating and the stationary member due to the difference in thermalexpansion therebetween.

[0018] In this rotary machine, it is preferable to dispose a ridgeopposite to at least one of the sealing fins, the ridge having a widthgreater than the thickness of the sealing fins along the axis ofrotation. Thus, a possibility of maintaining a small clearance betweenthe ridge and the sealing fin is higher than that of maintaining a smallclearance between sealing fins when the rotating member and thestationary member are displaced axially relative to each other due tothe difference in thermal expansion therebetween.

[0019] In this sealing device, the plurality of sealing fins are firstfins opposite to the ridge, and second fins other than the first finsand it is preferable that the first fins are arranged at pitches smallerthan those at which the second fins are arranged. Thus, the number ofthe first fns that are possible to maintain a small clearance can beincreased to enhance the sealing performance.

[0020] In this rotary machine, the unequal pitches of the sealing finscan be determined by using, for example, an elementary function.

[0021] Preferably, this rotary machine further comprises a moving meansfor axially moving at least the sealing fins disposed on one side of thegap. The positions of the sealing fins can be corrected by axiallymoving the sealing fins by the moving means when the rotating member andthe stationary member are displaced axially relative to each other dueto the difference in thermal expansion (thermal contraction)therebetween. Thus, it is possible to further effectively suppress thedeterioration of sealing performance resulting from the relative axialdisplacement of the rotating member and the stationary member due to thedifference in thermal expansion (thermal contraction) therebetween.

[0022] According to the present invention, there is also provided arotary machine comprising: a rotating member supported for rotationabout an axis of rotation; a stationary member surrounding the rotatingmember; a sealing device provided on at least one of the rotating memberand the stationary member, the sealing device having a sealing memberprojecting at a certain axial position into a gap between the rotatingmember and the stationary member; and a moving means for axially movingthe sealing member.

[0023] According to this rotary machine, the position of the sealingdevice can be corrected when the rotating member and the stationarymember are displaced axially relative to each other due to thedifference in thermal expansion (thermal contraction) therebetween byaxially moving the sealing member by the moving means. Thus, it ispossible to suppress the deterioration of sealing performance resultingfrom the relative axial displacement of the rotating member and thestationary member due to the difference in thermal expansion (thermalcontraction) therebetween.

[0024] In this rotary machine, the sealing device may further include asupport member provided on the stationary member to support the sealingmember, and the moving means may be a spring interposed between thestationary member and the support member.

[0025] Preferably, the spring is formed of a shape memory alloyexpanding and contracting according to temperature changes. Thus, thesealing member can axially be moved by utilizing temperature changes atthe start and at the stoppage of the rotary machine.

[0026] The shape memory alloy forming the spring is selected from, forexample, Ti—Ni alloys, Cu—Zn alloys, Ni—Al alloys and Fe—Mn alloys.Springs formed of those shape memory alloys extend with the rise oftemperature.

[0027] In one embodiment of this rotary machine, the spring is exposedto a high-temperature working fluid flowing through the gap between therotating member and the stationary member and is disposed on an upstreamside of the support member with respect to a flowing direction of theworking fluid. When the spring is formed of a shape memory alloy thatextends with the rise of temperature (contracts with the drop oftemperature), the position of the sealing device can be corrected at thestart of the rotary machine when the sealing device is relativelydisplaced upstream with respect to the flowing direction of the workingfluid with the rise of temperature due to the difference in thermalexpansion between the rotating member and the stationary member. Theposition of the sealing device can be corrected at the stoppage of therotary machine when the sealing device is relatively displaceddownstream with respect to the flowing direction of the working fluidwith the drop of temperature due to the difference in thermal expansionbetween the rotating member and the stationary member.

[0028] In another embodiment of this rotary machine, the spring isexposed to a high-temperature working fluid flowing through the gapbetween the rotating member and the stationary member and is disposed ona downstream side of the support member with respect to a flowingdirection of the working fluid. When the spring is formed of a shapememory alloy that extends with the drop of temperature (contracts withthe rise of temperature), the position of the sealing device can becorrected at the stop of the rotary machine when the sealing device isrelatively displaced downstream with respect to the flowing direction ofthe working fluid with the drop of temperature due to the difference inthermal expansion between the rotating member and the stationary member,and the position of the sealing device can be corrected at the start ofthe rotary machine when the sealing device is relatively displacedupstream with respect to the flowing direction of the working fluid withthe rise of temperature due to the difference in thermal expansionbetween the rotating member and the stationary member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a typical sectional view of an essential part of arotary machine in a first embodiment according to the present invention;

[0030]FIG. 2 is a graph showing the variation of working fluid leak-rateratio with relative axial displacement of opposite sealing fins in asealing device included in a general rotary machine;

[0031]FIG. 3 is a graph showing the variation of the leak rate of aworking fluid with the number of fins forming a narrower clearance in asealing device included in a general rotary machine;

[0032]FIG. 4 is a typical sectional view of an essential part of arotary machine in a second embodiment according to the presentinvention;

[0033]FIG. 5 is a typical sectional view of an essential part of arotary machine in a third embodiment according to the present invention;

[0034]FIG. 6 is a typical sectional view of an essential part of arotary machine in a fourth embodiment according to the presentinvention;

[0035]FIG. 7 is a typical sectional view of an essential part of arotary machine in a fifth embodiment according to the present invention;

[0036]FIG. 8 is a half longitudinal sectional view of a general steamturbine, i.e. a rotary machine;

[0037]FIG. 9 is an enlarged view of a part of the steam turbine shown inFIG. 8;

[0038]FIG. 10 is a typical sectional view of a comb-type labyrinthsealing device included in a conventional rotary machine;

[0039]FIG. 11 is a longitudinal sectional view of an essential part of arotary machine provided with a conventional sealing device;

[0040]FIG. 12 is a sectional view taken on the line A-A in FIG. 11;

[0041]FIG. 13 is a longitudinal sectional view of an essential part of arotary machine provided with another conventional sealing device; and

[0042]FIG. 14 is a sectional view taken on the line B-B in FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

[0043] Preferred embodiments of the present invention will be describedwith reference to the drawings. FIGS. 1, and 4 to 7 show rotary machinesin preferred embodiment according to the present invention.

FIRST EMBODIMENT

[0044] A rotary machine in a first embodiment according to the presentinvention will be described with reference to FIG. 1. FIG. 1 shows anessential part of the rotary machine in the first embodiment, such as anaxial-flow turbine. The rotary machine has a rotor 1 supported forrotation about an axis of rotation and provided with a rotor blade 2,i.e. a rotating member, and a labyrinth packing 9, i.e. a stationarymember, surrounding the rotor 1. The labyrinth packing 9 is held on anouter ring 3 of a nozzle diaphragm mounted on a casing 6 (FIGS. 8 and9). A comb-type labyrinth sealing device S1 is disposed in a gap betweenthe outer edge of the rotor blade 2 and the labyrinth packing 9.

[0045] The labyrinth sealing device S1 has a plurality of sealing finsF1 and F2 arranged opposite to each other on the opposite sides of thegap, respectively. The sealing fins F1 and F2 are axially spaced apartat unequal pitches. More specifically, the sealing fins F1 and F2 of therotary machine in the first embodiment are arranged such that the pitchbetween the adjacent sealing fins increases gradually in one axialdirection.

[0046] Since the sealing fins are axially spaced apart at unequalpitches, a possibility that some of the clearances between the oppositesealing fins F1 and F2 decrease when the rotator 1 and the casing 6(FIG. 8) are axially displaced relative to each other due to thedifference in thermal expansion between the rotor 1 and the casing 6increases. Therefore, the sealing device of the rotary machine in thefirst embodiment, as compared with the sealing device in which all thesealing fins are arranged at equal pitches, is capable of suppressingthe deterioration of sealing performance resulting from the relativeaxial displacement of the rotor 1 and the casing 6 due to the differencein thermal expansion between the rotor 1 and the casing 6.

[0047] The labyrinth sealing device Si differs from the conventionallabyrinth sealing device only in the arrangement of the sealing fins.Thus, the labyrinth sealing device S1 can be obtained through theimprovement of the sealing performance of the conventional labyrinthsealing device without entailing much increase in the manufacturingcost, and is capable of improving the performance of the rotary machine.

[0048] The effect of the first embodiment will be verified withreference to graphs shown in FIGS. 2 and 3.

[0049]FIG. 2 is a graph showing the variation of working fluid leak-rateratio with relative axial displacement of opposite sealing fins in asealing device included in a general rotary machine. The working fluidleak-rate ratios are ratios of leak rates to that when the relativeaxial displacement is 0.0 mm. Sealing fins on the side of a rotatingmember are axially spaced apart at equal pitches and those on the sideof a stationary member are axially spaced apart at equal pitchesdifferent from those between the sealing fins on the side of therotating member. As obvious from FIG. 2, the working fluid leak-rateratio has a general tendency to increase with the increase of therelative axial displacement, and increase in the working fluid leak-rateratio is suppressed or the working fluid leak-rate ratio decreases atrelative axial displacements of about 9.6, about 19.2 and about 28.8 mm.It is inferred that such a mode of variation of the working fluidleak-rate ratio occurs because the sealing fins on the side of therotating member and those on the side of the stationary member arearranged at different pitches, respectively, and hence small clearancesare formed between some of the opposite sealing fins when the relativeaxial displacement is equal to an integral multiple of 9.6 mm.

[0050]FIG. 3 is a graph showing the variation of working fluid leak-rateratio with the number N of fins forming a narrower clearance B (=A/2, Ais a clearance formed by the rest of the sealing fins) in a sealingdevice included in a general rotary machine. The working fluid leak-rateratios are ratios of leak rates to that when the number N=0. The numberof the sealing fins on the side of the rotating member and that of thesealing fins on the side of the stationary member are five. In FIG. 3,“CL=A” denotes a state where all the sealing fins are arranged so thatall the clearances between the opposite sealing fins are equal to theclearance A, “CL=B” denotes a state where all the sealing fins arearranged so that all the clearances between the opposite sealing finsare equal to the clearance B=A/2, “Upstream-side tightening” denotes astate where only the clearance between one opposite pair of the sealingfins at the upstream end, with respect to the flowing direction of theworking fluid, of the arrangement of the sealing fins is B=A/2, and theclearances between the other four opposite pairs of sealing fins are A.“Downstream-side tightening” denotes a state where only the clearancebetween one opposite pair of the sealing fins at the downstream end,with respect to the flowing direction of the working fluid, of thearrangement of the sealing fins is B=A/2, and the clearances between theother four opposite pairs of sealing fins are A. “Intermediatetightening” denotes a state where the clearances between the second andthe fourth opposite pairs of sealing fins, from the upstream side withrespect to the flowing direction of the working fluid are B=A/2, and theclearances between the other three opposite pairs of sealing fins are A.The graph shown in FIG. 3 indicates that the working fluid leak-rateratio decreases and sealing performance is enhanced with the increase ofthe number of the sealing fins forming the narrower clearances when thetotal number of the sealing fins is fixed.

[0051] As apparent form the foregoing description, according to thefirst embodiment, a possibility increases that some of the clearancesbetween the opposite sealing fins decrease, and thereby thedeterioration of the sealing performance resulting from the relativeaxial displacement of the rotor blade 2 and the labyrinth packing 9 dueto the difference in thermal expansion can be suppressed. In the sealingdevice relevant to the data shown in FIG. 2, the sealing fins on therotating member are axially spaced apart at equal pitches, and thesealing fins on the stationary member are axially spaced at equalpitches different from those at which the sealing fins on the rotatingmember are spaced apart. On the other hand, the sealing fins of thesealing device included in the rotary machine in the first embodimentare axially spaced apart at the unequal pitches. The sealing devicehaving the fins axially spaced apart at the unequal pitches in the firstembodiment is more effective in increasing a possibility that some ofthe clearances between the opposite sealing fins decreases than thesealing device relevant to the data shown in FIG. 2.

SECOND EMBODIMENT

[0052] A rotary machine in a second embodiment according to the presentinvention will be described with reference to FIG. 4. The rotary machinein the second embodiment is provided with a labyrinth sealing device S2.The labyrinth sealing device S2 is the same in construction as thelabyrinth sealing device S1 in the first embodiment shown in FIG. 1,except that the labyrinth sealing device S2 differs from the labyrinthsealing device S1 in the arrangement of its sealing fins F1 and F2.

[0053] In the sealing device S2 included in the rotary machine in thesecond embodiment, the sealing fins F1 on the side of a rotor blade 2are axially spaced apart at unequal pitches such that the pitchesdecrease from both ends toward the middle of the row of the sealing finsF1. The sealing fins F2 on the side of a labyrinth packing 9 are axiallyspaced apart at unequal pitches such that the pitches decrease from oneend toward the middle of the row of the sealing fins F2, increase in themiddle of the row, decrease again in the middle of the row, and thenincrease toward the other end of the row.

[0054] The sealing device included in the rotary machine in the secondembodiment provided with the sealing fins F1 and F2 axially spaced apartat the unequal pitches, similarly to the sealing device in the firstembodiment, is capable of suppressing the deterioration of sealingperformance resulting from the relative axial displacement of the rotorblade 2 and the labyrinth packing 9 due to the difference in thermalexpansion.

MODIFICATIONS OF THE FIRST AND THE SECOND EMBODIMENT

[0055] Although the sealing fins F1 and F2 are arranged at the unequalpitches on the opposite side, respectively, of the gap in the first andthe second embodiment, the effect of the present invention can beachieved by arranging only either the sealing fins F1 or the sealingfins F2 at the unequal pitches on one side of the gap.

THIRD EMBODIMENT

[0056] A rotary machine in a third embodiment according to the presentinvention will be described with reference to FIG. 5. The rotary machinein the third embodiment is provided with a labyrinth sealing device S3.The labyrinth sealing device S3 differs from the labyrinth sealingdevice S1 in the first embodiment shown in FIG. 1 in that a ridge 35 isformed in the outer edge of a rotor blade 2 and some of the sealing finsF2 are disposed opposite to the ridge 35. The ridge 35 has a widthgreater than the thickness of sealing fins F1 and F2 (F2′) along theaxis of rotation. The labyrinth sealing device S3 is similar in otherrespects to the labyrinth sealing device Si included in the rotarymachine in the first embodiment.

[0057] The sealing fins F1 on the rotor blade 2 provided with the ridge35 are axially space apart substantially at equal pitches. Pitchesbetween the sealing fins F2′ (first sealing fins) opposite to the ridge35 among the sealing fins F2 are smaller than those between the othersealing fins F2 (second sealing fins).

[0058] A possibility that the clearance between the ridge 35 and thesealing fins F2′ facing the ridge 35 remains smaller than those betweenthe sealing fins F1 and F2 is high when the rotor blade 2 and thelabyrinth packing 9 are displaced axially relative to each other due tothe difference in thermal expansion. Accordingly, the capability of thelabyrinth sealing device S3 to suppress the deterioration of sealingperformance due to the relative axial displacement of the rotatingmember and the stationary member is higher than those of the labyrinthsealing devices S1 and S2 in the first and the second embodiment.

[0059] Since the pitches between the sealing fins F2′ facing the ridge35 are smaller than those between the other sealing fins F2, anincreased number of the sealing fins F2′ can be arranged opposite to theridge 35 to improve the sealing performance of the labyrinth sealingdevice S3.

[0060] The labyrinth sealing device S3 includes the single ridge 35 onthe rotor blade 2, a plurality of ridges 35 may be formed on the rotorblade 2 or the labyrinth packing 9. Although the four sealing fins F2are disposed opposite to the ridge 35 in FIG. 5, any suitable number ofthe sealing fins F1 or the sealing fins F2 may be disposed opposite tothe ridge 35.

MODIFICATIONS OF THE FIRST TO THE THIRD EMBODIMENT

[0061] Although the sealing fins F1 and F2 are arranged in axial rowssuch that fin density in one or two parts of the axial row is higherthan those in other parts of the axial row in the labyrinth sealingdevices S1, S2 and S3 in the first to the third embodiment, the sealingfins F1 and f2 may be arranged in axial rows such that fin density inmore than two parts of the axial row may be higher than those in otherparts of the axial row. The unequal pitches between the sealing fins F1and F2 may be determined by using an elementary function, such as anexponential function or a trigonometric function. When an exponentialfunction is used, it is desirable that coefficient of exponent is notsmaller than 1.0 and less than 10.

[0062] Although the labyrinth sealing devices S1, S2 and S3 are disposedin the gap between the labyrinth packing 9 mounted on the outer ring 3of the nozzle diaphragm and the outer edge of the rotor blade 2 in thefirst to the third embodiment, the labyrinth sealing devices S1, S2 andS3 may be disposed in a gap between the outer ring of the nozzlediaphragm and the stator blade or a casing body and the rotor for thesame effect.

[0063] Although the sealing fins F1 and F2 of the labyrinth sealingdevices in the first to the third embodiment are extendedperpendicularly to the axis of rotation, the sealing fins F1 and F2 maybe inclined upstream to the axis of rotation for the further improvementof sealing performance.

FOURTH EMBODIMENT

[0064] A rotary machine in a fourth embodiment according to the presentinvention will be described with reference to FIG. 6 showing anessential part of the rotary machine, such as an axial-flow turbine.This rotary machine includes a rotor 1 supported for rotation about anaxis of rotation, and an inner ring 5 of a nozzle diaphragm providedwith a labyrinth packing 22, i.e. a stationary member, surrounding therotor 1. The inner ring 5 is held on a casing 6 via an outer ring 3 ofthe nozzle diaphragm and a stator blade 4 (FIGS. 8 and 9).

[0065] A labyrinth sealing device generally called a hi-lo labyrinthsealing device is disposed in a gap between the labyrinth packing 22 andthe rotor 1. The labyrinth sealing device includes a plurality of longsealing fins (sealing members) 26 a and short sealing fins (sealingmembers) 26 b held on the labyrinth packing (support member) 22, and aplurality of ridges 19 formed on the side surface of the rotor 1. Thelong sealing fins 26 a and the short sealing fins 26 b are arrangedalternately so as to project toward the rotor 1. The ridges 19 of therotor 1 are arranged opposite the short sealing fins 26 b. For example,the sealing fins 26 a and 26 b and the ridges 19 are arranged axially atequal pitches.

[0066] The inner ring 5 of the nozzle diaphragm is provided with acircumferential groove 23 for holding the labyrinth packing 22 therein.Annular ridges 24 a and 24 b project from the opposite side surfaces ofthe groove 23, respectively. The labyrinth packing 22 is provided withgrooves. 25 a and 25 b in its opposite axial end surfaces, respectively.The ridges 24 a and 24 b are received in the grooves 25 a and 25 b,respectively. A coil spring 27 is placed in the groove 25 a on theupstream side with respect to the flowing direction of steam ST, i.e.hot working fluid. The coil spring 27 serves as a moving means foraxially moving the labyrinth packing 22 to move the fins 26 a and 26 baxially relative to the inner ring 5 of the nozzle diaphragm.

[0067] The spring 27 is formed of a shape memory alloy and capable ofextending when its temperature rises and of contracting when itstemperature falls. Suitable shape memory alloys for forming the spring27 are Ti—Ni alloys, Cu—Zn alloys, Ni—Al alloys and Fe—Mn alloys.

[0068] The operation of the rotary machine thus constructed will beexplained. Both the rotor 1 and the casing 6 (FIG. 8) extend downstreamwith respect to the flowing direction of steam ST as temperature risesat the start of the rotary machine. The rate of thermal extension of thecasing 6 is lower than that of the rotor 1 due to the difference in heatcapacity between the rotor 1 and the casing 6. Consequently, the innerring 5 of the nozzle diaphragm, which is held on the casing 6 via theouter ring 3 of the nozzle diaphragm and the stator blade 4 (FIGS. 8 and9), moves upstream with respect to the flowing direction of steam STrelative to the rotor 1 by a distance corresponding to the differencebetween the respective thermal extensions of the rotor 1 and the casing6.

[0069] In this state, the spring 27 placed in the groove 25 a on theupstream side of the labyrinth packing 22 with respect to the flowingdirection of steam ST is exposed to steam ST in the groove 23 and isheated by steam ST. Consequently, the length of the spring 27 increasesas its temperature rises to move the labyrinth packing 22 downstreamwith respect to the flowing direction of steam ST relative to the innerring 5 of the nozzle diaphragm. Thus, the positions of the fins 26 a and26 b are corrected to compensate for the upstream displacement of thesealing fins 26 a and 26 b due to the difference in thermal expansionbetween the rotor 1 and the casing 6.

[0070] Both the rotor 1 and the casing 6 (FIG. 8) contract upstream withrespect to the flowing direction of steam ST as temperature falls at thestoppage of the rotary machine. The rate of thermal contraction of thecasing 6 is lower than that of the rotor 1 due to the difference in heatcapacity between the rotor 1 and the casing 6. Consequently, the innerring 5 of the nozzle diaphragm moves downstream with respect to theflowing direction of steam ST relative to the rotor 1.

[0071] In this state, the spring 27 placed in the groove 25 a on theupstream side of the labyrinth packing 22 with respect to the flowingdirection of steam ST moves the labyrinth packing 22 upstream withrespect to the flowing direction of steam ST relative to the inner ring5 of the nozzle diaphragm as its temperature falls. Thus, the positionsof the fins 26 a and 26 b are corrected to compensate for the downstreamdisplacement of the sealing fins 26 a and 26 b due to the difference inthermal contraction between the rotor 1 and the casing 6.

FIFTH EMBODIMENT

[0072] A rotary machine in a fifth embodiment according to the presentinvention will be described with reference to FIG. 7. This rotarymachine differs from the rotary machine in the fourth embodiment in thata coil spring 27′ is placed in a groove 25 b, on the downstream sidewith respect to the flowing direction of steam ST, formed in a labyrinthpacking 22 and the coil spring 27′ is formed of a shape memory alloycapable of contracting when its temperature rises and of extending whenits temperature falls. The rotary machine in the fifth embodiment is thesame in other respects as the rotary machine in the fourth embodimentshown in FIG. 6.

[0073] At the start of the rotary machine, the spring 27′ contracts asits temperature rises to move the labyrinth packing 22 downstream withrespect to the flowing direction of steam ST relative to the inner ring5 of the nozzle diaphragm. Thus, the positions of the fins 26 a and 26 bare corrected to compensate for the upstream displacement of the sealingfins 26 a and 26 b due to the difference in thermal expansion betweenthe rotor 1 and the casing 6.

[0074] At the stoppage of the rotary machine he spring 27′ moves thelabyrinth packing 22 upstream with respect to the flowing direction ofsteam ST relative to the inner ring 5 of the nozzle diaphragm as itstemperature falls. Thus, the positions of the fins 26 a and 26 b arecorrected to compensate for the downstream displacement of the sealingfins 26 a and 26 b due to the difference in thermal contraction betweenthe rotor 1 and the casing 6.

MODIFICATIONS OF THE FOURTH AND THE FIFTH EMBODIMENT

[0075] Although the labyrinth sealing device is disposed in the gapbetween the inner ring 5 of the nozzle diaphragm and the rotor 1 in thefourth and the fifth embodiment, the labyrinth sealing device may bedisposed in a gap between the outer ring of the nozzle diaphragm and arotor blade or in a gap between the casing body and the rotor.

[0076] Although the labyrinth sealing devices in the fourth and thefifth embodiment include the springs 27 and 27′ formed of the shapememory alloys, as the moving means, respectively, the moving means maybe a spring formed of any other material, and a spring other than thecoil spring may be used. The labyrinth sealing device of the presentinvention may employ, for example, a hydraulic cylinder actuator insteadof the spring as a moving means.

Other Embodiments

[0077] One of the first to the third embodiment, and either the fourthor the fifth embodiment may be used in combination. In the labyrinthsealing devices employed in the first to the third embodiment may beprovided with the moving means employed in the fourth or the fifthembodiment to move the sealing fins axially. Thus, the relative axialdisplacement of the sealing fins due to the difference in thermalexpansion (contraction) between the rotating member and the stationarymember can be corrected to suppress the deterioration of sealingperformance.

1. A rotary machine comprising: a rotating member supported for rotationabout an axis of rotation; a stationary member surrounding the rotatingmember; and a sealing device disposed in a gap between the rotatingmember and the stationary member, wherein the sealing device includes aplurality of sealing fins arranged opposite to each other on theopposite sides of the gap, and at least the sealing fins arranged on oneside of the gap are axially spaced apart at unequal pitches.
 2. Therotary machine according to claim 1, wherein a ridge is disposedopposite to at least one of the sealing fins, the ridge having a widthgreater than thickness of the sealing fins along the axis of rotation.3. The rotary machine according to claim 2, wherein the plurality ofsealing fins are first fins opposite to the ridge and second fins otherthan the first fins, and the first fins are arranged at pitches smallerthan those at which the second fins are arranged.
 4. The rotary machineaccording to claim 1, wherein the unequal pitches of the sealing finsare determined by using an elementary function.
 5. The rotary machineaccording to claim 1, further comprising a moving means for axiallymoving at least the sealing fins disposed on one side of the gap.
 6. Arotary machine comprising: a rotating member supported for rotationabout an axis of rotation; a stationary member surrounding the rotatingmember; a sealing device provided on at least one of the rotating memberand the stationary member, the sealing device having a sealing memberprojecting at a certain axial position into a gap between the rotatingmember and the stationary member; and a moving means for axially movingthe sealing member.
 7. The rotary machine according to claim 6, whereinthe sealing device further include a support member provided on thestationary member to support the sealing member, and the moving means isa spring interposed between the stationary member and the supportmember.
 8. The rotary machine according to claim 7, wherein the springis formed of a shape memory alloy expanding and contracting according totemperature changes.
 9. The rotary machine according to claim 8, whereinthe shape memory alloy forming the spring is selected from Ti—Ni alloys,Cu—Zn alloys, Ni—Al alloys and Fe—Mn alloys.
 10. The rotary machineaccording to claim 8, the spring is exposed to a high-temperatureworking fluid flowing through the gap between the rotating member andthe stationary member and is disposed on an upstream side of the supportmember with respect to a flowing direction of the working fluid.
 11. Therotary machine according to claim 8, wherein the spring is exposed to ahigh-temperature working fluid flowing through the gap between therotating member and the stationary member and is disposed on adownstream side of the support member with respect to a flowingdirection of the working fluid.